1. Field of the Invention
The present invention relates to a motion picture projector apparatus with film speed changing apparatus.
2. Description of the Prior Art
Generally speaking, for the driving source of a motion picture projection apparatus, an induction motor or the like is mainly used. The rotation speed n of this motor is generally expressed by the equation n = 120 f/p (rpm) where p represents the number of poles and f the frequency of the current source. As is clear from the above mentioned equation, the rotation speeds are different from each other when an induction motor is driven by a current source having different frequencies. However, there are no standard frequencies of the commercial current source in the world, for example, in the United States, the frequency of the commercial current source is 60 Hz while in Europe that of the commercial current source is 50 Hz.
Therefore, when the motion picture projection apparatus with the film feeding mechanism, whose induction motor is so designed that the film can be fed at a proper speed with the commercial current source of 60 Hz, is driven with the commercial current source of 50 Hz, the speed of the rotation is smaller by one sixth than when the induction motor is driven with the commercial current source of 60 Hz. In consequence, the speed of the pictures to be projected is lowered proportionally so that the motion picture projected does not seem natural. Even if such deleterious influence upon the motion picture projected can be tolerated, there may occur a problem with the sound motion picture projection apparatus by means of which sound regenerating means the sound information stored in one part of the film is picked up and regenerated at the same time.
Therefore, in order to solve the above mentioned problem today, it is proposed to alter the ratio of the transmission from the induction motor to the film feeding mechanism in accordance with the frequencies of the commercial current source then used. Hereby the conventional method to alter the ratio of the transmission is for example, to fix a pulley with V-shaped or U-shaped groove on the motor shaft respectively on the rotary shaft of the film feeding mechanism and to provide between these pulleys a properly shaped belt so as to adapted in the grooves of the pulleys in such a manner that the driving power is transmitted from the motor to the film feeding mechanism, whereby there are following various methods:
a. a method to exchange either the pulley fixed on the motor shaft or that fixed on the rotary shaft of the film feeding mechanism for a pulley with a groove of different diameter, changing at the same time the belt or a method to exchange either the pulley fixed on the motor shaft or that fixed on the rotary shaft of the film feeding mechanism for a pulley with a groove of different diameter, without changing the belt, or
b. as the method not to put out the pulley fixed on the rotary shaft from the shaft each time, a pulley on which a plural number of grooves with different diameters are formed as one body along the axial direction of the rotary shaft is fixed on the rotary shaft in advance and only the position of the pulley grooves on which the belt is to be provided is changed in accordance with the frequencies of the commercial current source without taking out the pulley from the shaft.
However, according to the conventional method, when the apparatus is used at a place where the frequency of the commercial current source is different, the cover has to be taken off every time when the frequency differs. Further, in the former case, the pulley has to be completely exchanged for the other pulley so that, not only is it troublesome, but also the spare pulleys have to be prepared because at least more than two kinds of pulleys have to be reserved. Further even in the latter case, after the cover having being taken off, the position of the belt is changed, which is also troublesome.
Further, quite recently in order to meet the demand for a motion picture projection apparatus whose projection speed, namely the number of pictures per second, can be altered in order to increase the efficiency of the motion picture projection apparatus. Such apparatus has begun to appear on the market.
The method to change the number of the pictures per second when a motion picture projection apparatus in which the frequency can not be changed easily, namely the pulley fixed on the rotary shaft of the motor, is completely changed is to form the groove of the pulley fixed on the rotary shaft flat and at the same time to form the pulley fixed on the rotary shaft of the film feeding mechanism in such a manner that a plural number of the pulley parts with flat engaging parts on which the belt is provided extends along the axial direction of the rotary shaft. The parts between the pulley parts are tapered whereby the number of pictures per second can be altered by engaging the belt with the pulley parts of different diameter in accordance with the number of pictures per second to be chosen.
Further, a motion picture projection apparatus, which presents a number of picture changing mechanisms by means of which the frequency change for adjusting the speed of the induction motor under the influence of the difference of the frequency and the change of the number of picture per second are possible also exists, whereby the driving power is not transmitted from the motor directly to the film feeding mechanism by means of one belt but is transmitted to the third rotary shaft provided between the rotary shaft of the motor and that of the film feeding mechanism by means of a belt and at the same time from the third rotary shaft to the rotary shaft of the film feeding mechanism by means of another belt, namely the change frequency is effected between the rotary shaft of the motor and the third rotary shaft while the change of the number of picture is effected between the third rotary shaft and the rotary shaft of the film feeding mechanism. In consequence, as a result of these methods, many components are necessary so that not only the mechanism becomes complicated but also the manufacturing cost becomes high. Further, the driving power is transmitted from the motor to the film feeding mechanism in two steps, namely by means of two belts so that the loss of energy due to the slip between every belt and due the rotary shaft and to the contact of large area between each belt and the rotary shaft is remarkable. There it becomes necessary to provide a motor having large capacity taking the above into consideration, which results in further lack of economy.